Modified silicon-carbon laminate lithium battery and formation method thereof

Abstract

The present disclosure provides a modified silicon-carbon laminated lithium battery and its formation method. In the above-mentioned formation method, a highly elastic three-dimensional conductive mesh is formed in the silicon-based negative electrode sheet of the modified silicon-carbon laminated lithium battery, and it is a polymer diaphragm; the modified silicon-carbon laminated lithium battery injected with liquid is sequentially subjected to a first stage of low-temperature, low-voltage, small-current constant-current charging operation, a second stage of low-temperature, medium-voltage, medium-current constant-current charging operation, a third stage of high-temperature, high-voltage, large-current constant-current charging operation, and a fourth stage of low-temperature, high-voltage, large-current constant-current discharge operation, and finally a room-temperature static operation. The above-mentioned method enables the polymer diaphragm to change with the temperature change of the formation process, and the added highly elastic three-dimensional conductive mesh can effectively suppress the expansion and peeling problem of the silicon-based negative electrode of the high-energy, high-rate laminated lithium battery during the formation process, and also increases the elastic modulus of the negative electrode active material layer, reduces expansion deformation, and improves the cycle performance and high-rate performance of the modified silicon-carbon laminated lithium battery.

Description

Technical Field

[0001] The present disclosure relates to the technical field of laminated lithium batteries, and in particular to a modified silicon-carbon laminated lithium battery and a formation method thereof. Background Art

[0002] Generally, battery capacity depends on the positive electrode material. To maximize the positive electrode performance of laminated lithium batteries, they are typically stacked in an alternating "negative-positive-negative" stacking process to fully utilize the positive electrode material. However, this results in lithium ions only being intercalated on the side of the two outermost silicon-based negative electrodes corresponding to the positive electrode, while the other side, facing away from the positive electrode, remains free of lithium ions. When the laminated lithium battery is fully charged, the lithium ion intercalation causes the volume of the silicon-based negative electrode corresponding to the positive electrode to expand, creating a significant stress differential between the two outermost silicon-based negative electrodes. This can cause the negative electrode active material to peel away from the negative electrode current collector. This phenomenon is particularly pronounced after pressure charging to full charge. The peeled negative electrode active material can easily pierce the separator, causing safety issues. Alternatively, the peeled negative electrode active material can become free within the battery, causing self-discharge and impacting battery performance.

[0003] To this end, some scholars believe that the above-mentioned problems can be solved by optimizing the formation process of silicon-based laminated lithium batteries. However, for example, Chinese patent document No. CN108258347B discloses a formation method for a silicon-anode soft-pack lithium-ion battery. By controlling the upper limit of the charging voltage in stages, applying mechanical external pressure to the battery, and applying negative pressure inside the battery, the uniform volume change of the silicon-based negative electrode during the charge and discharge process is controlled. This effectively improves the wrinkling problem of the silicon-based negative electrode in the lithium-ion soft-pack battery, but does not effectively suppress the expansion of the silicon-based negative electrode. For example, Chinese patent document No. CN117080594A discloses a formation method for a silicon-anode soft-pack lithium-ion battery. This method uses a full-charge formation process and gradually increases the pressure to improve the electrolyte utilization rate and facilitate the formation of a more uniform, stable and dense SEI film. However, it does not effectively suppress the expansion of the silicon-based negative electrode. Moreover, after pressurization, P3>P2, resulting in excessive pressure that damages the lithium battery internally and affects the cycle life of the lithium battery. It can be seen that the above-mentioned silicon-based laminated lithium battery formation process is still unable to effectively suppress the expansion and peeling problem of the silicon-based negative electrode during the formation process of high-energy and high-rate laminated lithium batteries. Summary of the Invention

[0004] The purpose of the present disclosure is to overcome the shortcomings of the prior art and provide a modified silicon-carbon laminated lithium battery and its formation method, in which a polymer diaphragm can change with the temperature change of the formation process, and the added high-elasticity wrapped three-dimensional conductive mesh can effectively suppress the expansion and peeling problem of the silicon-based negative electrode during the formation process of high-energy and high-rate laminated lithium batteries. At the same time, the elastic modulus of the negative electrode active material layer is increased, and the expansion deformation is reduced, thereby improving the high-temperature cycle performance and high-rate performance of the modified silicon-carbon laminated lithium battery.

[0005] The purpose of this disclosure is achieved through the following technical solutions:

[0006] A modified silicon-carbon laminate lithium battery comprises the following steps:

[0007] Obtaining a modified silicon-carbon laminated lithium battery filled with liquid; wherein a highly elastic three-dimensional conductive mesh is formed in the negative electrode active material layer of the silicon-based negative electrode sheet of the modified silicon-carbon laminated lithium battery, and the highly elastic three-dimensional conductive mesh is used to inhibit expansion and peeling of the silicon-carbon material; and the separator of the modified silicon-carbon laminated lithium battery is a polymer separator;

[0008] The modified silicon-carbon laminated lithium battery injected with liquid is subjected to a first stage of low-temperature, low-voltage, small-current constant-current charging operation to charge the modified silicon-carbon laminated lithium battery to 15% to 20% SOC;

[0009] The modified silicon-carbon laminated lithium battery that has undergone the first stage of low-temperature, low-voltage, small-current constant-current charging operation is subjected to a second stage of low-temperature, medium-voltage, medium-current constant-current charging operation, so that the modified silicon-carbon laminated lithium battery is charged to 40% to 60% SOC;

[0010] Performing a third stage of high-temperature, high-voltage, high-current, constant-current charging on the modified silicon-carbon laminated lithium battery that has undergone the second stage of low-temperature, medium-voltage, medium-current constant-current charging operation, so that the modified silicon-carbon laminated lithium battery is charged to 100% SOC;

[0011] The modified silicon-carbon laminated lithium battery that has undergone the third stage of high-temperature, high-voltage, high-current constant-current charging operation is subjected to a fourth stage of low-temperature, high-voltage, high-current constant-current discharging operation, so that the modified silicon-carbon laminated lithium battery is discharged to 30% to 50% DOD;

[0012] The modified silicon-carbon laminated lithium battery that has undergone the fourth stage of low-temperature, high-voltage, large-current constant-current discharge operation is subjected to a room-temperature static operation.

[0013] In one embodiment, the first stage of low-temperature, low-voltage, small-current constant-current charging operation is performed under the conditions of a pressure F1 of 1 kgf / cm2 to 2 kgf / cm2, a temperature of 30°C to 40°C, and a current of 0.1C to 0.2C.

[0014] In one embodiment, the second stage low-temperature, medium-voltage, medium-current constant-current charging operation is performed under the conditions of a pressure F2 of 3kgf / cm2 to 4kgf / cm2, a temperature of 30°C to 40°C, and a current of 0.3C to 0.4C.

[0015] In one embodiment, the third stage of high temperature, high pressure, large current constant current charging operation is performed under the conditions of pressure F3 of 6kgf / cm2 to 8kgf / cm2, temperature of 80℃ to 90℃, and current of 0.5C to 1.0C.

[0016] In one embodiment, the fourth stage of low-temperature, high-voltage, and high-current constant-current discharge is performed under the conditions of a pressure F4 of 6 kgf / cm2 to 8 kgf / cm2, a temperature of 30°C to 40°C, and a current of 0.5C to 1.0C.

[0017] In one embodiment, the time of the room temperature static operation is 1 hour to 4 hours.

[0018] In one embodiment, the negative electrode active material layer includes graphite, silicon-carbon material, linear single-walled carbon nanotubes, mesh carbon fibers, and a highly elastic binder;

[0019] The linear single-walled carbon nanotubes, the mesh carbon fibers and the highly elastic binder are mixed to form the highly elastic wound three-dimensional conductive mesh;

[0020] The highly elastic wound three-dimensional conductive mesh is mixed with the silicon-carbon material and the graphite to obtain a negative electrode slurry; and the negative electrode slurry is coated on a negative electrode current collector to form the negative electrode active material layer.

[0021] In one embodiment, the length of the linear single-walled carbon nanotube is 8 nm to 10 nm; and / or,

[0022] The length of the mesh carbon fiber is 100um to 200um; and / or,

[0023] The highly elastic binder includes at least one of PMA, PAA and SBR.

[0024] A modified silicon-carbon laminate lithium battery is prepared by the formation method of the modified silicon-carbon laminate lithium battery described in any of the above embodiments.

[0025] In one embodiment, the modified silicon-carbon laminate lithium battery includes a shell and a battery cell, the battery cell is arranged in the shell, and the battery cell includes a plurality of alternately stacked silicon-based negative electrode sheets, positive electrode sheets and silicon-based negative electrode sheets, the silicon-based negative electrode sheets are separated from the positive electrode sheets by a diaphragm, and the diaphragm extends to the outer side surfaces of the silicon-based negative electrode sheets located on the outermost sides of the battery cell.

[0026] Compared with the prior art, the present disclosure has at least the following advantages:

[0027] 1) The first stage of low-temperature, low-voltage, small-current constant-current charging operation, the second stage of low-temperature, medium-voltage, medium-current constant-current charging operation, and the third stage of high-temperature, high-voltage, large-current constant-current charging operation are adopted to realize the slow charging operation of the modified silicon-carbon laminated lithium battery in stages, so as to avoid the problem of the silicon-carbon material expanding too fast and causing expansion and peeling due to excessive charging of the modified silicon-carbon laminated lithium battery; at the same time, when the modified silicon-carbon laminated lithium battery is fully charged to 100% SOC, it is ensured that the active materials in the modified silicon-carbon laminated lithium battery can achieve full, comprehensive and rapid reaction, that is, the modified silicon-carbon laminated lithium battery is easier to form under fully charged conditions, which is conducive to the modification. A uniform protective interface film is formed inside the modified silicon-carbon laminated lithium battery, thereby improving the high-rate performance and high-temperature cycle performance of the modified silicon-carbon laminated lithium battery; and the added fourth low-temperature, high-voltage, and high-current constant-current discharge operation enables the modified silicon-carbon laminated lithium battery to discharge to 30% to 50% DOD. On the one hand, it reduces the stress difference between the silicon-based negative electrode sheets on the outermost sides of the cell of the modified silicon-carbon laminated lithium battery, and effectively reduces the phenomenon of the negative electrode active material peeling off the negative electrode current collector; on the other hand, it also better ensures that the liquid retention volume of the modified silicon-carbon laminated lithium battery at this time is sufficient, so as to ensure that a more uniform protective interface film is formed inside the modified silicon-carbon laminated lithium battery.

[0028] 2) Since a highly elastic wound three-dimensional conductive mesh is formed in the negative active material layer of the silicon-based negative electrode sheet, the highly elastic wound three-dimensional conductive mesh plays a restraining role at the beginning stage of the expansion of the silicon-carbon material, so as to more comprehensively restrain the expansion of the internal silicon-carbon material that restrains the negative active material layer; effectively reduces the expansion rate of the silicon-based negative electrode sheet itself; especially in conjunction with the optimization process disclosed in the present invention, it can more effectively restrain the expansion and peeling problem of the silicon-carbon material; and, the added highly elastic wound three-dimensional conductive mesh improves the conductive performance of the silicon-based negative electrode sheet, so as to improve the conductive ability of the negative active material layer, which is beneficial to improving the high-rate performance of the modified silicon-carbon laminated lithium battery, while also increasing the elastic modulus of the negative active material layer, reducing expansion deformation, and thus improving the high-temperature cycle performance of the modified silicon-carbon laminated lithium battery.

[0029] 3) Since the diaphragm of the modified silicon-carbon laminated lithium battery is a polymer diaphragm, the surface of the polymer diaphragm can be softened as the temperature of the formation process increases. When the modified silicon-carbon laminated lithium battery is in the third stage of high-temperature, high-voltage, high-current constant-current charging operation, the expansion rate of the silicon-carbon material is the largest at this time, so that the softened polymer diaphragm can better bond with the expanded silicon-carbon material, effectively avoiding the expansion and peeling of the silicon-carbon material under the maximum expansion rate condition, and further suppressing the expansion and peeling problem of the silicon-carbon material; and, when the modified silicon-carbon laminated lithium battery is in the fourth stage of low-temperature, high-voltage, high-current constant-current discharge operation, the polymer diaphragm will gradually harden and lose its viscosity due to the drop in temperature, which is conducive to a more comprehensive peeling of the polymer diaphragm and the silicon-carbon material, effectively avoiding the negative electrode active material layer adhering to the polymer diaphragm and affecting the cycle performance of the modified silicon-carbon laminated lithium battery, and cooperating with the use of the highly elastic wrapped three-dimensional conductive mesh and the optimized process disclosed in the present invention, the expansion and peeling problem of the silicon-based negative electrode in the formation process of the high-energy and high-rate laminated lithium battery can be more effectively suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0031] Figure 1 This is a flow chart of a modified silicon-carbon laminate lithium battery according to one embodiment of the present invention;

[0032] Figure 2 This is a comparison diagram of the expansion of the modified silicon-carbon laminate lithium battery of Example 2 of the present invention and Comparative Example 14;

[0033] Figure 3 This is a charge and discharge curve diagram at different rates of Example 2 of the present invention. DETAILED DESCRIPTION

[0034] To facilitate understanding of the present disclosure, a more comprehensive description of the present disclosure will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present disclosure. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure.

[0035] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly attached to the other element or there may be an intermediate element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure pertains. The terms used herein in the specification of this disclosure are intended only to describe specific embodiments and are not intended to limit this disclosure. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0037] The present disclosure provides a formation method for a modified silicon-carbon laminated lithium battery, and obtains a modified silicon-carbon laminated lithium battery filled with liquid; wherein, a highly elastic three-dimensional conductive network is formed in the negative electrode active material layer of the silicon-based negative electrode sheet of the modified silicon-carbon laminated lithium battery, and the highly elastic three-dimensional conductive network is used to inhibit the expansion and peeling of the silicon-carbon material; the diaphragm of the modified silicon-carbon laminated lithium battery is a polymer diaphragm; the modified silicon-carbon laminated lithium battery filled with liquid is subjected to a first stage of low-temperature, low-voltage, small-current constant-current charging operation to charge the modified silicon-carbon laminated lithium battery to 15% to 20% SOC; the modified silicon-carbon laminated lithium battery that has undergone the first stage of low-temperature, low-voltage, small-current constant-current charging operation is subjected to a second stage of low-temperature, low-voltage, small-current constant-current charging operation to charge the modified silicon-carbon laminated lithium battery to 15% to 20% SOC; A medium-voltage, medium-current constant-current charging operation is performed to charge the modified silicon-carbon laminate lithium battery to 40% to 60% SOC; a third-stage, high-temperature, high-voltage, and high-current constant-current charging operation is performed on the modified silicon-carbon laminate lithium battery that has undergone the second-stage, low-temperature, medium-voltage, and medium-current constant-current charging operation to charge the modified silicon-carbon laminate lithium battery to 100% SOC; a fourth-stage, low-temperature, high-voltage, and high-current constant-current discharge operation is performed on the modified silicon-carbon laminate lithium battery that has undergone the third-stage, high-temperature, high-current constant-current charging operation to discharge the modified silicon-carbon laminate lithium battery to 30% to 50% DOD; the modified silicon-carbon laminate lithium battery that has undergone the fourth-stage, low-temperature, high-voltage, and high-current constant-current discharge operation is performed at room temperature.

[0038] The above-mentioned modified silicon-carbon laminated lithium battery formation method reduces the expansion rate of the silicon-based negative electrode sheet itself while optimizing the polymer diaphragm so that the polymer diaphragm can change with the temperature change of the formation process, that is, the polymer diaphragm softens during the third stage of high-temperature, high-voltage, high-current constant-current charging operation, so that the softened polymer diaphragm can better bond with the expanded silicon-carbon material, effectively avoiding the expansion and peeling of the silicon-carbon material under the condition of maximum expansion rate, and further suppressing the expansion and peeling problem of the silicon-carbon material; and the polymer diaphragm will slowly soften due to the temperature drop during the fourth stage of low-temperature, high-voltage, high-current constant-current discharge operation. Slowly hardening to make the polymer lose its stickiness is conducive to a more comprehensive peeling of the polymer diaphragm and the silicon-carbon material, effectively avoiding the negative electrode active material layer from adhering to the polymer diaphragm and affecting the cycle performance of the modified silicon-carbon laminated lithium battery, so as to more effectively suppress the expansion and peeling of the silicon-based negative electrode in the formation process of the high-energy and high-rate laminated lithium battery. In addition, the added high-elasticity wrapped three-dimensional conductive mesh not only improves the conductivity of the negative electrode active material layer, which is conducive to improving the high-rate performance of the modified silicon-carbon laminated lithium battery, but also increases the elastic modulus of the negative electrode active material layer, reduces expansion deformation, and thus improves the high-temperature cycle performance of the modified silicon-carbon laminated lithium battery.

[0039] See also Figure 1 To better understand the technical solutions and beneficial effects of the present disclosure, the present disclosure is further described in detail below in conjunction with specific embodiments. A modified silicon-carbon laminated lithium battery in one embodiment includes some or all of the following steps:

[0040] S101. Obtain a modified silicon-carbon laminated lithium battery filled with liquid; wherein, a highly elastically wound three-dimensional conductive mesh is formed in the negative electrode active material layer of the silicon-based negative electrode sheet of the modified silicon-carbon laminated lithium battery, and the highly elastically wound three-dimensional conductive mesh is used to inhibit the expansion and peeling of the silicon-carbon material; the diaphragm of the modified silicon-carbon laminated lithium battery is a polymer diaphragm.

[0041] It is understandable that there are currently some Chinese patent documents that suppress the volume expansion of silicon-based negative electrodes by optimizing the structure of silicon-based negative electrodes, thereby improving the cycle performance, safety and high-current charge and discharge capabilities of silicon-based lithium-ion batteries. For example, Chinese patent document No. CN111129427B discloses a silicon-based negative electrode and a preparation method thereof, which adds a functional coating on the active material layer so that the polypyrrole, single-walled carbon nanotubes and carboxymethyl cellulose lithium of the functional coating can form a three-dimensional mesh-like conductive network to achieve a cage effect on the volume expansion of the silicon-based negative electrode, thereby suppressing the volume expansion of the silicon-based negative electrode. However, since the functional coating is directly reacted and formed on the active material layer, that is, the functional coating is formed and fixed on one side of the active material layer, the functional coating will only play an inhibitory role when the active material layer expands to a large extent, and it is impossible to achieve a better inhibitory and binding effect on the inside of the active material layer, and there is still a probability of silicon-carbon material expansion and peeling.

[0042] Therefore, in the present disclosure, a highly elastic wound three-dimensional conductive mesh is formed within the negative electrode active material layer, so that the highly elastic wound three-dimensional conductive mesh plays a restraining role at the beginning stage of the expansion of the silicon-carbon material, thereby more comprehensively restraining the expansion of the internal silicon-carbon material that restrains the negative electrode active material layer; effectively reducing the expansion rate of the silicon-based negative electrode sheet itself; thereby effectively reducing the probability of expansion and peeling of the silicon-carbon material, and also reducing the side reactions of the modified silicon-carbon laminated lithium battery at high temperature, thereby improving the high temperature performance of the modified silicon-carbon laminated lithium battery while taking into account the improvement of the energy density of the modified silicon-carbon laminated lithium battery.

[0043] It should be noted that while the addition of a highly elastic, wound, three-dimensional conductive mesh can effectively suppress the expansion of the silicon-based anode sheet, due to the approximately 300% higher expansion coefficient of the silicon-carbon material, simply optimizing the silicon-based anode material structure still cannot effectively suppress the expansion of the silicon-carbon material in some high-energy, high-rate laminated lithium batteries. This is especially true when fully charged in high-energy, high-rate laminated lithium batteries, where the silicon-carbon material is fully embedded with lithium and expands to its maximum extent. The presence of pores in the highly elastic, wound three-dimensional conductive mesh creates the possibility that a small amount of silicon-carbon material will expand and peel off the pores of the highly elastic, wound three-dimensional conductive mesh.

[0044] Therefore, in the present disclosure, by adopting a polymer membrane, the added polymer membrane can change with the temperature change of the formation process, that is, the polymer membrane softens during the third stage of high temperature, high pressure, large current constant current charging operation, and the softened polymer membrane can better bond with the expanded silicon-carbon material, effectively avoiding the expansion and peeling of the silicon-carbon material under the condition of maximum expansion rate, and further suppressing the problem of expansion and peeling of the silicon-carbon material; and the polymer membrane will slowly harden due to the drop in temperature during the fourth stage of low temperature, high pressure, large current constant current discharge operation to make the polymer lose its viscosity, which is conducive to a more comprehensive peeling of the polymer membrane and the silicon-carbon material, effectively avoiding the negative electrode active material layer adhering to the polymer membrane and affecting the cycle performance of the modified silicon-carbon laminated lithium battery, so as to more effectively suppress the expansion and peeling problem of the silicon-based negative electrode of the high-energy and high-rate laminated lithium battery during the formation process.

[0045] S102. Perform the first stage of low-temperature, low-voltage, small-current constant-current charging operation on the modified silicon-carbon laminated lithium battery that has been filled with liquid, so that the modified silicon-carbon laminated lithium battery is charged to 15% to 20% SOC; this is to achieve the first stage of slow charging operation of the modified silicon-carbon laminated lithium battery, so as to avoid the problem of the modified silicon-carbon laminated lithium battery expanding too fast due to over-rapid charging, thereby causing expansion and peeling, and also to achieve preliminary heating of the polymer diaphragm.

[0046] S103. The modified silicon-carbon laminated lithium battery that has undergone the first stage of low-temperature, low-voltage, small-current constant-current charging operation is subjected to a second stage of low-temperature, medium-voltage, medium-current constant-current charging operation, so that the modified silicon-carbon laminated lithium battery is charged to 40% to 60% SOC, so as to achieve a faster charging operation of the modified silicon-carbon laminated lithium battery in the second stage, so as to avoid the problem of the silicon-carbon material expanding too fast and causing expansion and peeling due to over-rapid charging of the modified silicon-carbon laminated lithium battery; and also achieve secondary heating of the polymer diaphragm.

[0047] S104. The modified silicon-carbon laminated lithium battery that has undergone the second stage of low-temperature, medium-voltage, medium-current constant-current charging operation is subjected to a third stage of high-temperature, high-voltage, large-current constant-current charging operation, so that the modified silicon-carbon laminated lithium battery is charged to 100% SOC, so as to achieve a faster charging operation of the modified silicon-carbon laminated lithium battery in the third stage, so as to avoid the problem of the modified silicon-carbon laminated lithium battery expanding too fast due to excessive charging, thereby causing expansion and peeling.

[0048] It can be understood that when the modified silicon-carbon laminated lithium battery is fully charged to 100% SOC, it is ensured that the active materials in the modified silicon-carbon laminated lithium battery can achieve full, comprehensive and rapid reaction, that is, the modified silicon-carbon laminated lithium battery is easier to form under fully charged conditions, especially in conjunction with the first low-temperature, low-voltage, small current constant current charging operation, the second low-temperature, medium-voltage, medium current constant current charging operation and the third high-temperature, high-voltage, large current constant current charging operation, which is conducive to the formation of a uniform protective interface film inside the modified silicon-carbon laminated lithium battery, thereby improving the high-rate performance and high-temperature cycle performance of the modified silicon-carbon laminated lithium battery.

[0049] It can also be understood that when the modified silicon-carbon laminated lithium battery is fully charged to 100% SOC, the expansion rate of the silicon-carbon material is the largest at this time, and the polymer surface of the polymer membrane can be softened. In this way, the softened polymer membrane can better bond with the expanded silicon-carbon material, effectively avoiding the expansion and peeling of the silicon-carbon material under the condition of maximum expansion rate, and further suppressing the problem of expansion and peeling of the silicon-carbon material.

[0050] S105, performing a fourth stage of low-temperature, high-voltage, high-current constant-current discharge operation on the modified silicon-carbon laminated lithium battery that has undergone the third stage of high-temperature, high-voltage, high-current constant-current charge operation, so that the modified silicon-carbon laminated lithium battery is discharged to 30% to 50% DOD.

[0051] It can be understood that when the modified silicon-carbon laminated lithium battery is in the fourth stage of low-temperature, high-voltage, and high-current constant-current discharge operation, the modified silicon-carbon laminated lithium battery is discharged to 30% to 50% DOD. On the one hand, it reduces the stress difference between the silicon-based negative electrodes on the outermost sides of the cell of the modified silicon-carbon laminated lithium battery, and effectively reduces the phenomenon of the negative electrode active material peeling off the negative electrode current collector; on the other hand, it also better ensures that the liquid retention of the modified silicon-carbon laminated lithium battery is sufficient at this time, so as to ensure that a more uniform protective interface film is formed inside the modified silicon-carbon laminated lithium battery; on the other hand, due to the drop in temperature, the polymer diaphragm It will slowly harden and lose its stickiness, which is conducive to a more comprehensive peeling of the polymer diaphragm and the silicon-carbon material, effectively avoiding the negative electrode active material layer adhering to the polymer diaphragm and affecting the cycle performance of the modified silicon-carbon laminated lithium battery, so as to more effectively suppress the expansion and peeling of the silicon-based negative electrode in the formation process of the high-energy and high-rate laminated lithium battery; on the other hand, it also achieves a faster cooling of the modified silicon-carbon laminated lithium battery, effectively avoiding the problem of decomposition and destruction of the protective interface film or volatilization of the organic solvent in the electrolyte caused by the modified silicon-carbon laminated lithium battery being under high temperature conditions for a long time.

[0052] S106. The modified silicon-carbon laminated lithium battery that has undergone the fourth stage of low-temperature, high-voltage, and high-current constant-current discharge operation is placed at room temperature to allow the electrolyte to well infiltrate the battery cells of the modified silicon-carbon laminated lithium battery, which is beneficial to the normal discharge of the modified silicon-carbon laminated lithium battery, thereby ensuring that the silicon-carbon material can shrink well under room temperature conditions, effectively avoiding the appearance of many wrinkles in the modified silicon-carbon laminated lithium battery; at the same time, it is also beneficial to form a denser and more uniform protective interface film inside the modified silicon-carbon laminated lithium battery.

[0053] The above-mentioned formation method of the modified silicon-carbon laminated lithium battery adopts the first stage of low-temperature, low-voltage, small-current constant-current charging operation, the second stage of low-temperature, medium-voltage, medium-current constant-current charging operation and the third stage of high-temperature, high-voltage, large-current constant-current charging operation to realize the slow charging operation of the modified silicon-carbon laminated lithium battery in stages, so as to avoid the problem of the silicon-carbon material expanding too fast and causing expansion and peeling due to over-fast charging of the modified silicon-carbon laminated lithium battery; at the same time, when the modified silicon-carbon laminated lithium battery is fully charged to 100% SOC, it is ensured that the active materials in the modified silicon-carbon laminated lithium battery can achieve full, comprehensive and rapid reaction, that is, the modified silicon-carbon laminated lithium battery is more likely to react under fully charged conditions. Easy formation is conducive to the formation of a uniform protective interface film inside the modified silicon-carbon laminated lithium battery, thereby improving the high-rate performance and high-temperature cycle performance of the modified silicon-carbon laminated lithium battery; and the added fourth stage of low-temperature, high-voltage, and high-current constant-current discharge operation enables the modified silicon-carbon laminated lithium battery to discharge to 30% to 50% DOD. On the one hand, it reduces the stress difference between the silicon-based negative electrode sheets on the outermost sides of the cell of the modified silicon-carbon laminated lithium battery, and effectively reduces the phenomenon of the negative electrode active material peeling off the negative electrode current collector; on the other hand, it also better ensures that the liquid retention volume of the modified silicon-carbon laminated lithium battery at this time is sufficient, so as to ensure that a more uniform protective interface film is formed inside the modified silicon-carbon laminated lithium battery.

[0054] It can be understood that since a highly elastic wound three-dimensional conductive mesh is formed within the negative active material layer of the silicon-based negative electrode sheet, the highly elastic wound three-dimensional conductive mesh plays a restraining role at the beginning of the expansion of the silicon-carbon material, so as to more comprehensively restrain the expansion of the internal silicon-carbon material that restrains the negative active material layer; effectively reducing the expansion rate of the silicon-based negative electrode sheet itself; especially in conjunction with the optimized process disclosed herein, the problem of expansion and peeling of the silicon-carbon material is more effectively suppressed; and the added highly elastic wound three-dimensional conductive mesh improves the conductive properties of the silicon-based negative electrode sheet, thereby improving the conductive capacity of the negative active material layer, which is beneficial to improving the high-rate performance of the modified silicon-carbon laminated lithium battery, while also increasing the elastic modulus of the negative active material layer, reducing expansion deformation, and thus improving the high-temperature cycle performance of the modified silicon-carbon laminated lithium battery. For details, please refer to Figure 3 .

[0055] It can also be understood that, since the diaphragm of the modified silicon-carbon laminated lithium battery is a polymer diaphragm, the surface of the polymer diaphragm can be softened as the temperature of the formation process increases. When the modified silicon-carbon laminated lithium battery is in the third stage of high-temperature, high-voltage, high-current constant-current charging operation, the expansion rate of the silicon-carbon material at this time is the largest, so that the softened polymer diaphragm can better bond with the expanded silicon-carbon material, effectively avoiding the phenomenon of expansion and peeling of the silicon-carbon material under the condition of the maximum expansion rate, and further suppressing the problem of expansion and peeling of the silicon-carbon material; and, when the modified silicon-carbon laminated lithium battery is During the fourth stage of low-temperature, high-voltage, and high-current constant-current discharge operation, the polymer diaphragm gradually hardens and loses its viscosity due to the drop in temperature, which is conducive to a more comprehensive peeling of the polymer diaphragm and the silicon-carbon material, effectively preventing the negative electrode active material layer from adhering to the polymer diaphragm and affecting the cycle performance of the modified silicon-carbon laminated lithium battery. In conjunction with the use of a highly elastically wound three-dimensional conductive mesh and the optimized process disclosed herein, the problem of expansion and peeling of the silicon-based negative electrode in the formation process of high-energy and high-rate laminated lithium batteries can be more effectively suppressed, that is, the expansion rate of the modified silicon-carbon laminated lithium battery after formation is relatively small. For details, please refer to Figure 2 .

[0056] In one embodiment, the modified silicon-carbon laminated lithium battery is subjected to a vacuum sealing operation after being left to stand at room temperature to effectively remove the gas in the modified silicon-carbon laminated lithium battery and perform sealing.

[0057] In one embodiment, the pressure F1 is 1 kgf / cm 2 ~2kgf / cm 2 The first stage of low-temperature, low-voltage, small-current constant-current charging operation is carried out under the conditions of temperature of 30℃~40℃ and current of 0.1C~0.2C. While realizing the first stage slow charging operation of the modified silicon-carbon laminated lithium battery, it also realizes the preliminary heating of the polymer membrane.

[0058] In one embodiment, when the pressure F2 is 3 kgf / cm 2 ~4kgf / cm 2 The second stage of low-temperature, medium-voltage, medium-current constant-current charging operation is carried out under the conditions of temperature of 30℃~40℃ and current of 0.3C~0.4C. While realizing the second stage faster charging operation of the modified silicon-carbon laminated lithium battery, it also realizes the secondary heating of the polymer membrane.

[0059] In one embodiment, the pressure F3 is 6 kgf / cm 2 ~8kgf / cm 2The third stage of high-temperature, high-voltage, high-current constant-current charging operation is carried out under the conditions of a temperature of 80°C to 90°C and a current of 0.5C to 1.0C, thereby achieving a faster charging operation of the third stage of the modified silicon-carbon laminated lithium battery, so that the modified silicon-carbon laminated lithium battery is easier to form under a fully charged condition; at the same time, it also ensures that the polymer surface of the polymer diaphragm can be softened, so that the softened polymer diaphragm can better bond to the expanded silicon-carbon material, effectively avoiding the expansion and peeling of the silicon-carbon material under the condition of the maximum expansion rate, and further suppressing the expansion and peeling problem of the silicon-carbon material.

[0060] It should be noted that the general formation temperature of lithium-ion batteries is 30℃~60℃. When the formation temperature is higher than 60℃, it will cause the protective interface film in the modified silicon-carbon laminated lithium battery to decompose and destroy or the organic solvent in the electrolyte to volatilize. Therefore, in order to solve the above problems, in this disclosure, 6kgf / cm 2 ~8kgf / cm 2 The high voltage and high current of 0.5C~1.0C are used for constant current fast charging to effectively shorten the time of the third stage of high temperature, high pressure and high current constant current charging operation, thereby ensuring that the modified silicon-carbon laminated lithium battery can reach 100% SOC within 1min~2min. In particular, it is combined with the fourth stage of low temperature, high pressure and high current constant current discharge operation to effectively avoid the problem that the modified silicon-carbon laminated lithium battery is easily decomposed and damaged in the protective interface film or the organic solvent in the electrolyte is volatilized under long high temperature conditions. The fourth stage of low temperature, high pressure and high current constant current discharge operation is still a large current, which not only saves charging time, but also improves the utilization rate of the formation equipment.

[0061] Furthermore, in one embodiment, the electrolyte is a high temperature resistant electrolyte to avoid the problem of the electrolyte being easily decomposed and destroyed under high temperature conditions.

[0062] In one embodiment, the pressure F4 is 6 kgf / cm 2 ~8kgf / cm 2 The fourth stage of low-temperature, high-voltage, and high-current constant-current discharge is carried out under the conditions of a temperature of 30°C to 40°C and a current of 0.5C to 1.0C. On the premise of ensuring that the stress difference of the silicon-based negative electrodes on the outermost sides of the modified silicon-carbon laminated lithium battery cell after discharge is small, it also ensures that the liquid retention of the modified silicon-carbon laminated lithium battery is sufficient, which is conducive to forming a more uniform protective interface film; it also makes the polymer diaphragm lose its viscosity as the temperature drops as the fourth stage, which is conducive to a more comprehensive peeling with the silicon-carbon material; it also achieves a faster cooling of the modified silicon-carbon laminated lithium battery, effectively avoiding the problem of decomposition and destruction of the protective interface film or volatilization of the organic solvent in the electrolyte caused by the modified silicon-carbon laminated lithium battery being under high temperature conditions for a long time.

[0063] In one embodiment, the time of the room temperature static operation is 1 hour to 4 hours.

[0064] In one embodiment, the polymer membrane is a PVDF polymer membrane. Since PVDF is an adhesive used for silicon-based negative or positive electrodes, the added PVDF polymer will not affect the electrical properties of the modified silicon-carbon laminated lithium battery. Moreover, when the PVDF polymer membrane is in the third stage of high-temperature, high-pressure, and high-current constant-current charging operation at 80°C to 90°C, the polymer surface of the polymer membrane can be softened, while the interior of the PVDF layer and the base membrane of the PVDF polymer membrane will not be deformed.

[0065] In one embodiment, the PVDF polymer separator includes a base film and a PVDF layer coated on the base film. Specifically, the thickness of the PVDF layer is 2 μm to 3 μm to ensure that the PVDF is well softened at 80° C. to 90° C.

[0066] In one embodiment, the molecular weight of PVDF is 400,000 Da to 600,000 Da, so as to ensure that the PVDF polymer is well softened at 80° C. to 90° C.

[0067] In one embodiment, the negative electrode active material layer includes graphite, silicon-carbon material, linear single-walled carbon nanotubes, mesh carbon fibers and a highly elastic binder; wherein the linear single-walled carbon nanotubes, the mesh carbon fibers and the highly elastic binder are mixed to form the highly elastic wound three-dimensional conductive mesh; the highly elastic wound three-dimensional conductive mesh is mixed with the silicon-carbon material and the graphite to obtain a negative electrode slurry; and the negative electrode slurry is coated on a negative electrode current collector to form the negative electrode active material layer.

[0068] It can be understood that by using mesh carbon fibers as a matrix, adding linear single-walled carbon nanotubes and a highly elastic binder under mixing conditions, a highly elastic wound three-dimensional conductive mesh can be formed, and then the highly elastic wound three-dimensional conductive mesh is mixed with graphite and silicon-carbon materials, so that the highly elastic wound three-dimensional conductive mesh can wrap the silicon-carbon material and graphite, that is, the highly elastic wound three-dimensional conductive mesh is mixed inside the negative electrode active material layer, thereby effectively reducing the expansion rate of the silicon-based negative electrode sheet itself.

[0069] In one embodiment, the length of the linear single-walled carbon nanotubes is 8nm to 10nm; in particular, the length of the mesh carbon fibers is 100um to 200um and the high-elasticity binder includes at least one of PMA (Propylene Glycol Methyl Ether Acetate), PAA (Polyacrylic Acid) and SBR (Styrene-Butadiene Rubber), so as to ensure the formation of a highly elastic entangled three-dimensional conductive network.

[0070] In one embodiment, the mass percentage of PMA is 0.3% to 1%, the mass percentage of PAA is 1% to 1.5%, and the mass percentage of SBR is 1.2% to 2%.

[0071] In a preferred embodiment, the highly elastic binder is a mixture of PMA, PAA, and SBR to ensure that the highly elastic binder has a high elastic modulus, thereby increasing the elastic modulus of the silicon-based anode material and effectively suppressing the expansion of the silicon-based anode material. Specifically, the weight percentages of PMA, PAA, and SBR are 0.3:1:1.5.

[0072] Specifically, the linear single-walled carbon nanotubes, the mesh carbon fibers and the high-elasticity binder are mixed at a stirring speed of 3000 r / min to 4000 r / min for 30 min to 60 min to ensure the formation of a highly elastic wound three-dimensional conductive network; the highly elastic wound three-dimensional conductive network is mixed with graphite and silicon-carbon materials at a stirring speed of 5000 r / min to 6000 r / min for 100 min to 120 min to obtain a negative electrode slurry.

[0073] In one embodiment, the negative electrode active material layer includes the following mass percentages: 81.2% to 85.5% graphite; 13% to 16% silicon-carbon material, 0.1% to 0.5% linear single-walled carbon nanotubes, 0.4% to 0.8% mesh carbon fibers and 1% to 1.5% high-elasticity binder to improve the conductivity of the negative electrode active material layer, which is beneficial to improving the high-rate performance of the modified silicon-carbon laminated lithium battery. At the same time, it also increases the elastic modulus of the negative electrode active material layer and reduces expansion deformation, thereby improving the high-temperature cycle performance of the modified silicon-carbon laminated lithium battery.

[0074] The present disclosure provides a modified silicon-carbon laminated lithium battery, prepared using the modified silicon-carbon laminated lithium battery formation method described in any of the above embodiments. It is understood that the formation method disclosed herein enables the polymer separator to change with temperature changes during the formation process. Simultaneously, the use of a highly elastic, wound three-dimensional conductive mesh effectively suppresses expansion and delamination of the silicon-based negative electrode during the formation process of high-energy, high-rate laminated lithium batteries. Furthermore, the elastic modulus of the negative electrode active material layer is increased, reducing expansion deformation, thereby improving the high-temperature cycling performance of the modified silicon-carbon laminated lithium battery.

[0075] In one embodiment, the modified silicon-carbon laminated lithium battery includes a shell and a battery cell, the battery cell is arranged in the shell, and the battery cell includes a plurality of alternately stacked silicon-based negative electrode sheets, positive electrode sheets and silicon-based negative electrode sheets to fully utilize the positive electrode material, thereby ensuring the preparation of a high-energy and high-rate silicon-carbon laminated lithium battery; the silicon-based negative electrode sheet is separated from the positive electrode sheet by a diaphragm, and the diaphragm extends to the outer side surfaces of the silicon-based negative electrode sheets located on the outermost two sides of the battery cell; the two outermost silicon-based negative electrode sheets are provided with a PVDF layer on the side facing away from the positive electrode sheet, so that the PVDF layer changes with the temperature change of the formation process disclosed in the present invention, so as to effectively suppress the problem of silicon-carbon material peeling off on the side facing away from the positive electrode sheet of the two outermost silicon-based negative electrode sheets.

[0076] Compared with the prior art, the present disclosure has at least the following advantages:

[0077] 1) The first stage of low-temperature, low-voltage, small-current constant-current charging operation, the second stage of low-temperature, medium-voltage, medium-current constant-current charging operation, and the third stage of high-temperature, high-voltage, large-current constant-current charging operation are adopted to realize the slow charging operation of the modified silicon-carbon laminated lithium battery in stages, so as to avoid the problem of the silicon-carbon material expanding too fast and causing expansion and peeling due to excessive charging of the modified silicon-carbon laminated lithium battery; at the same time, when the modified silicon-carbon laminated lithium battery is fully charged to 100% SOC, it is ensured that the active materials in the modified silicon-carbon laminated lithium battery can achieve full, comprehensive and rapid reaction, that is, the modified silicon-carbon laminated lithium battery is easier to form under fully charged conditions, which is conducive to the modification. A uniform protective interface film is formed inside the modified silicon-carbon laminated lithium battery, thereby improving the high-rate performance and high-temperature cycle performance of the modified silicon-carbon laminated lithium battery; and the added fourth low-temperature, high-voltage, and high-current constant-current discharge operation enables the modified silicon-carbon laminated lithium battery to discharge to 30% to 50% DOD. On the one hand, it reduces the stress difference between the silicon-based negative electrode sheets on the outermost sides of the cell of the modified silicon-carbon laminated lithium battery, and effectively reduces the phenomenon of the negative electrode active material peeling off the negative electrode current collector; on the other hand, it also better ensures that the liquid retention volume of the modified silicon-carbon laminated lithium battery at this time is sufficient, so as to ensure that a more uniform protective interface film is formed inside the modified silicon-carbon laminated lithium battery.

[0078] 2) Since a highly elastic wound three-dimensional conductive mesh is formed in the negative active material layer of the silicon-based negative electrode sheet, the highly elastic wound three-dimensional conductive mesh plays a restraining role at the beginning stage of the expansion of the silicon-carbon material, so as to more comprehensively restrain the expansion of the internal silicon-carbon material that restrains the negative active material layer; effectively reduces the expansion rate of the silicon-based negative electrode sheet itself; especially in conjunction with the optimization process disclosed in the present invention, it can more effectively restrain the expansion and peeling problem of the silicon-carbon material; and, the added highly elastic wound three-dimensional conductive mesh improves the conductive performance of the silicon-based negative electrode sheet, so as to improve the conductive ability of the negative active material layer, which is beneficial to improving the high-rate performance of the modified silicon-carbon laminated lithium battery, while also increasing the elastic modulus of the negative active material layer, reducing expansion deformation, and thus improving the high-temperature cycle performance of the modified silicon-carbon laminated lithium battery.

[0079] 3) Since the diaphragm of the modified silicon-carbon laminated lithium battery is a polymer diaphragm, the surface of the polymer diaphragm can be softened as the temperature of the formation process increases. When the modified silicon-carbon laminated lithium battery is in the third stage of high-temperature, high-voltage, high-current constant-current charging operation, the expansion rate of the silicon-carbon material is the largest at this time, so that the softened polymer diaphragm can better bond with the expanded silicon-carbon material, effectively avoiding the expansion and peeling of the silicon-carbon material under the maximum expansion rate condition, and further suppressing the expansion and peeling problem of the silicon-carbon material; and, when the modified silicon-carbon laminated lithium battery is in the fourth stage of low-temperature, high-voltage, high-current constant-current discharge operation, the polymer diaphragm will gradually harden and lose its viscosity due to the drop in temperature, which is conducive to a more comprehensive peeling of the polymer diaphragm and the silicon-carbon material, effectively avoiding the negative electrode active material layer adhering to the polymer diaphragm and affecting the cycle performance of the modified silicon-carbon laminated lithium battery, and cooperating with the use of the highly elastic wrapped three-dimensional conductive mesh and the optimized process disclosed in the present invention, the expansion and peeling problem of the silicon-based negative electrode in the formation process of the high-energy and high-rate laminated lithium battery can be more effectively suppressed.

[0080] Compared with the prior art, the present disclosure has at least the following advantages:

[0081] The following examples illustrate some specific embodiments, where percentages are expressed by weight. It should be noted that the following examples do not exhaust all possible situations, and that the materials used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0082] Table 1 Recipe

[0083]

[0084]

[0085] The formulations of Examples 1 to 3 and Comparative Examples 1 to 6 in Table 1 were prepared according to the following steps:

[0086] S1. Prepare the materials according to the formula in Table 1;

[0087] S2. Add linear single-walled carbon nanotubes, mesh carbon fibers, PMA, PAA, and SBR to a high-pressure mixer in sequence and stir and mix them. The stirring speed is controlled at 3000 r / min and the mixing time is 40 min. A highly elastic entangled three-dimensional conductive network is obtained.

[0088] S3, then add silicon carbon material and graphite and stir and mix, and control the stirring speed to 6000r / min; the mixing time is 100min; to obtain the negative electrode slurry;

[0089] S4, coating the negative electrode slurry on the negative electrode current collector and drying it to obtain a silicon-based negative electrode sheet;

[0090] S5. Stacking a plurality of silicon-based negative electrode sheets, a plurality of positive electrode sheets (high-nickel ternary positive electrode sheets), and a plurality of PVDF-based polymer separators in an alternating stacking process of negative electrode sheet-positive electrode sheet-negative electrode sheet, and extending the PVDF-based polymer separators to the outer side surfaces of the silicon-based negative electrode sheets located on the outermost sides of the battery cell; to prepare a modified silicon-carbon laminated lithium battery cell;

[0091] S5, encasing the modified silicon-carbon laminated lithium battery cell and injecting a high-temperature resistant electrolyte to obtain a modified silicon-carbon laminated lithium battery with electrolyte injection;

[0092] S6. Performing a fixture forming process on the modified silicon-carbon laminated lithium battery that has been injected with liquid;

[0093] S61, at a pressure of 1 kgf / cm 2 , the first stage of low-temperature, low-voltage, low-current constant-current charging operation is carried out at a temperature of 30°C and a current of 0.1C to 20% SOC;

[0094] S62, at pressure F2 of 4kgf / cm 2 , the second stage of low-temperature medium-voltage medium-current constant-current charging operation is carried out at a temperature of 40°C and a current of 0.4C to 60% SOC;

[0095] S63, at pressure F3 of 8kgf / cm 2 , the third stage of high temperature, high voltage, high current constant current charging operation is carried out at a temperature of 85°C and a current of 1.0C to 100% SOC;

[0096] S64, at pressure F4 of 8kgf / cm 2 , the fourth stage of low temperature, high voltage and high current constant current discharge is carried out to 50% DOD under the conditions of temperature 30℃ and current 1.0C;

[0097] S65, allowing the modified silicon-carbon laminated lithium battery after step S64 to stand at room temperature for 2 hours to complete the formation process;

[0098] S7, performing an evacuation and sealing operation on the modified silicon-carbon laminated lithium battery after step S65.

[0099] Comparative Example 7

[0100] The difference from Example 2 is that the S61 step is omitted in Comparative Example 7, and the rest remains unchanged.

[0101] Comparative Example 8

[0102] The difference from Example 2 is that in Comparative Example 8, step S62 is omitted, and the rest remains unchanged.

[0103] Comparative Example 9

[0104] The difference from Example 9 is that step S63 is omitted in Comparative Example 9, and the rest remains unchanged.

[0105] Comparative Example 10

[0106] The difference from Example 2 is that in Comparative Example 10, step S64 is omitted, and the rest remains unchanged.

[0107] Comparative Example 11

[0108] The difference from Example 2 is that the temperature in step S63 of Comparative Example 11 is 78° C., and the rest remain unchanged.

[0109] Comparative Example 12

[0110] The difference from Example 2 is that the temperature in step S63 of Comparative Example 12 is 92° C., and the rest remain unchanged.

[0111] Comparative Example 13

[0112] The difference from Example 2 is that the temperature in step S64 of Comparative Example 13 is 10° C., and the rest remain unchanged.

[0113] Comparative Example 14

[0114] The difference from Example 2 is that the diaphragm of Comparative Example 14 is a ceramic diaphragm, and the rest remains unchanged.

[0115] The modified silicon-carbon laminated lithium batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 14 were subjected to electrical performance tests as shown in Table 2 below to obtain the experimental data shown in Table 2.

[0116] Table 2

[0117]

[0118]

[0119] From the comparison of Examples 1 to 3 and Comparative Examples 1 to 2 in the above table, it can be seen that due to the simultaneous use of linear single-walled carbon nanotubes and mesh carbon fibers in Examples 1 to 3, the comprehensive indicators of Examples 1 to 3 are significantly better than those of Comparative Examples 1 to 2. Among them, the comprehensive indicators of Example 2 are the best.

[0120] From the comparison of Example 2 and Comparative Examples 3 to 5 in the above table, it can be seen that the comprehensive indicators of Example 2 are significantly better than those of Comparative Examples 3 to 5 because Example 2 uses PMA, PAA and SBR at the same time.

[0121] From the comparison between Example 2 and Comparative Example 6 in the above table, it can be seen that the comprehensive indicators of Example 2 are significantly better than those of Comparative Example 6 because Example 2 uses a PVDF polymer membrane.

[0122] From the comparison between Example 2 and Comparative Examples 7 to 10 in the above table, it can be seen that, since Example 2 adopts the chemical formation optimization process, the comprehensive indicators of Example 2 are significantly better than those of Comparative Examples 7 to 10.

[0123] From the comparison between Example 2 and Comparative Examples 11-12 in the above table, it can be seen that since the temperature of S63 in Example 2 is controlled at 80° C. to 90° C., the comprehensive indicators of Example 2 are significantly better than those of Comparative Examples 11-12.

[0124] From the comparison between Example 2 and Comparative Example 13 in the above table, it can be seen that since the temperature of S64 in Comparative Example 13 is lower than that of S64 in Example 2, the comprehensive indicators of Comparative Example 13 are significantly worse than those of Example 2.

[0125] From the comparison between Example 2 and Comparative Example 14 in the above table, it can be seen that since Comparative Example 14 is a ceramic diaphragm, it cannot effectively suppress the expansion of the modified silicon-carbon laminate lithium battery during the formation process, resulting in the comprehensive indicators of Comparative Example 14 being significantly worse than those of Example 2.

[0126] The above-described embodiments merely represent several implementation methods of the present disclosure. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the disclosed patent. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the scope of the present disclosure, all of which fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the disclosed patent shall be determined by the appended claims.

Claims

1. A formation method for a modified silicon-carbon laminate lithium battery, characterized in that: The steps include: Obtaining a modified silicon-carbon laminated lithium battery filled with liquid; wherein a highly elastic three-dimensional conductive mesh is formed in the negative electrode active material layer of the silicon-based negative electrode sheet of the modified silicon-carbon laminated lithium battery, and the highly elastic three-dimensional conductive mesh is used to inhibit expansion and peeling of the silicon-carbon material; and the separator of the modified silicon-carbon laminated lithium battery is a polymer separator; The negative electrode active material layer includes graphite, silicon-carbon material, linear single-walled carbon nanotubes, mesh carbon fibers and a highly elastic binder; The linear single-walled carbon nanotubes, the mesh carbon fibers and the highly elastic binder are mixed to form the highly elastic wound three-dimensional conductive mesh; The highly elastic wound three-dimensional conductive mesh is mixed with the silicon-carbon material and the graphite to obtain a negative electrode slurry; the negative electrode slurry is coated on a negative electrode current collector to form the negative electrode active material layer; The modified silicon-carbon laminated lithium battery injected with liquid is subjected to a first stage of low-temperature, low-voltage, small-current constant-current charging operation to charge the modified silicon-carbon laminated lithium battery to 15% to 20% SOC; wherein the temperature of the first stage of low-temperature, low-voltage, small-current constant-current charging operation is 30° C. to 40° C.; The modified silicon-carbon laminated lithium battery that has undergone the first low-temperature, low-voltage, small-current constant-current charging operation is subjected to a second low-temperature, medium-voltage, medium-current constant-current charging operation, so that the modified silicon-carbon laminated lithium battery is charged to 40% to 60% SOC; wherein the temperature of the second low-temperature, medium-voltage, medium-current constant-current charging operation is 30° C. to 40° C.; The modified silicon-carbon laminated lithium battery that has undergone the second stage of low-temperature, medium-voltage, medium-current constant-current charging operation is subjected to a third stage of high-temperature, high-voltage, high-current constant-current charging operation to charge the modified silicon-carbon laminated lithium battery to 100% SOC; wherein the temperature of the third stage of high-temperature, high-voltage, high-current constant-current charging operation is 80° C. to 90° C.; The modified silicon-carbon laminated lithium battery that has undergone the third stage of high-temperature, high-voltage, high-current constant-current charging operation is subjected to a fourth stage of low-temperature, high-voltage, high-current constant-current discharging operation, so that the modified silicon-carbon laminated lithium battery is discharged to 30% to 50% DOD; The modified silicon-carbon laminated lithium battery that has undergone the fourth stage of low-temperature, high-voltage, large-current constant-current discharge operation is subjected to a room-temperature static operation.

2. The formation method of the modified silicon-carbon laminate lithium battery according to claim 1, characterized in that: At a pressure of 1 kgf / cm 2 ~2kgf / cm 2 The first stage of low-temperature, low-voltage, small-current constant-current charging operation is carried out under the conditions of 0.1C~0.2C.

3. The formation method of the modified silicon-carbon laminate lithium battery according to claim 1, characterized in that: At pressure F2 of 3kgf / cm 2 ~4kgf / cm 2、 The second stage of low-temperature, medium-voltage, medium-current constant-current charging operation is carried out under the condition of current of 0.3C~0.4C.

4. The formation method of the modified silicon-carbon laminate lithium battery according to claim 1, characterized in that: At pressure F3 of 6 kgf / cm 2 ~8kgf / cm 2 The third stage of high temperature, high voltage, large current constant current charging operation is carried out under the conditions of current of 0.5C~1.0C.

5. The formation method of the modified silicon-carbon laminate lithium battery according to claim 1, characterized in that: At pressure F4 of 6kgf / cm 2 ~8kgf / cm 2 The fourth stage of low-temperature, high-voltage, and high-current constant-current discharge is carried out under the conditions of temperature of 30℃~40℃ and current of 0.5C~1.0C.

6. The formation method of the modified silicon-carbon laminate lithium battery according to claim 1, characterized in that: The time of the normal temperature standing operation is 1 hour to 4 hours.

7. The formation method of modified silicon-carbon laminate lithium battery according to claim 1, characterized in that: The length of the linear single-walled carbon nanotubes is 8 nm to 10 nm; and / or, The length of the mesh carbon fiber is 100um to 200um; and / or, The highly elastic binder includes at least one of PMA, PAA and SBR.

8. A modified silicon-carbon laminate lithium battery, characterized in that: The modified silicon-carbon laminate lithium battery is prepared by the formation method according to any one of claims 1 to 7.

9. The modified silicon-carbon laminate lithium battery according to claim 8, characterized in that: The modified silicon-carbon laminate lithium battery includes a shell and a battery cell. The battery cell is arranged in the shell. The battery cell includes a plurality of alternately stacked silicon-based negative electrode sheets, positive electrode sheets and silicon-based negative electrode sheets. The silicon-based negative electrode sheets are separated from the positive electrode sheets by a diaphragm, and the diaphragm extends to the outer side surfaces of the silicon-based negative electrode sheets located on the outermost sides of the battery cell.

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